Heater 12.6 volts at .15 amps or 6.3 volts at .3 amps.Two different triode systems equivalent to one half 12AX7 and one half 12AU7.
In the ECC823, Section 1 of the tube (pins 6, 7, and 8) is the low gain 12AU7/ECC82 spec (gain factor ~17) and Section 2 (pins 1, 2, and 3) is the high gain 12AX7/ECC83 spec (gain factor ~100).